Jet noise suppressor nozzle



Nov; 27, 1962 0 D r 3,065,818

JET NOISE SUPPRESSOR NOZZLE Filed Aug. 14, 1958 By 422: & 811M 7Altorneys United States Patent Britain Filed Aug. 14, 1958, Ser. No.754,958 Claims priority, application Great Britain Sept. 14, 1957 6Claims. (Cl. 18133) This invention relates to a jet noise suppressornozzle.

According to the present invention there is provided a jet noisesuppressor nozzle comprising a tubular member having a plurality ofhollow, flow-dividing members which are closed at their upstream endsand open at their downstream ends and which extend radially into the jetpath, the flow-dividing members being separated from each other bylongitudinal passages adapted for the flow of jet gases therethrough,alternate flow-dividing members extending radially inwardly to greaterand lesser extents.

Means are preferably provided for entraining atmospheric air, flowingexternally of the nozzle, into and through the interior of at least someof the flow-dividing members.

The means for entraining atmospheric air can comprise apertures in thetubular wall of the nozzle and guide vanes positioned across theapertures and shaped so as to direct atmospheric air into theflow-dividing members so that the air passes through the members and outof their downstream ends.

Preferably it is arranged that, at the downstream end of the nozzle, theratio of the two cross-sectional areas within the nozzle which arerespectively disposed externally and internally of the flow-dividingmembers are within the range 1:1.75 to 112.0.

If desired, the flow dividing members which extend furthest radially canbe braced by aerofoil struts interconnecting adjacent members.

Each flow-dividing member preferably increases in radial extent in adownstream direction.

The invention is illustrated, merely by way of example, in theaccompanying drawings, in which:

FIGURE 1 is a perspective view looking at the rear of a practicalembodiment of the nozzle according to the present invention, part of thenozzle being broken away to illustrate the construction more clearly;

FIGURE 2 is an elevation of a broken away part of the exterior of thenozzle of FIGURE '1 as seen in the direction of the arrow 2 of FIGURE 1and on the same scale; and

FIGURE 3 is a smaller scale diagrammatic side elevation of a gas turbineengine incorporating the nozzle of FIGURES 1 and 2.

The present invention is based upon the discovery that silencing isaifected by: (a) the ratio of the gas nozzle area to the atmosphericmixing air area. The first is the total of the cross-sectional areas (atthe downstream end of the nozzle) of the interiors of the flow dividingmembers, and the second being the whole crosssectional area of thenozzle at its downstream end less the first area, and (b) the diameterof the widest unobstructed outlet for the hot gases from the jet pipe.

As regards (a) it can be shown that the ratio should preferably be from1:1.75 to 1:20.

FIGURE 1 illustrates a nozzle which is in accordance with the presentinvention and which is designed to take' account of the factors a and blisted above. It will be seen that the nozzle has alternate flowdividing members 42, 43 which extend radially inwardly to greater andlesser extents. The arrangement of this figure is made such that theratio referred to in (a) above 3,065,818 Patented Nov. 27, 1962 is heldwithin the range 121.75 to 1:20. At the same time the dimension of thewidest unobstructed outlet for hot gases is held to the minimumpracticable value.

It will also be noted from FIGURE 1 that two inscribed circles could bedrawn which respectively touch the radially innermost portions of thealternate flow-dividing members 42, 43. This arrangement, thus providesin effect, a nozzle having a series of alternate deep and shallowcorrugations and therefore provides a very large total peripheral mixingarea about which mixing of the hot gases and atmospheric air occurswithout increasing the diameter of the smaller inscribed circle whichdefines the periphery of the hard core of hot gases which are the lastto mingle with atmospheric air and which, therefore, must be reduced tothe minimum. This circle also defines the widest unobstructed outlet forthe gases.

It has been found that the nozzle formation shown in FIGURE 1 enablesthe nozzle to be given a light, though rigid construction.

Referring now to FIGURE 1 as a practical embodiment of the invention,there is shown a jet noise suppressor nozzle 4i, having an externalcasing 41 through which flow hot gases from a jet pipe 50 (see FIGURE3), the direction of flow of the hot gases being indicated by the arrow39. Mounted within the external casing 41 are a number of hollowflow-dividing members 42, 43 which are closed at their upstream ends 37and open at their downstream ends 38 and which extend radially into thejet path. The members 42 and 43 alternate, the members 43 being ofconsiderably greater radial extent than the members 42.

Corresponding to each member 43 there is an aperture 44 (FIGURES l and2) in the casing 41 of the nozzle. Each aperture 44 has a pair of guidevanes 45 across it, the guide vanes being arranged to direct atmosphericair into the interior of the member 43 so that the air will flow out ofthe downstream end of the member 43. Apart from the apertures 44 and theopen downstream end, each member 43 is closed and increases in radialextent in a downstream direction.

Corresponding to each smaller member 42 there is, in the casing 41 ofthe nozzle, an aperture 46 and across each aperture 46 is a guide vane47 shaped to direct atmospheric air into the interior of the smallermembers 42, so that the air flows out through the open downstream endsof the members 42. The members 42 also increase in radial extent in adownstream direction.

Between the members 42 and 43 are formed channels 48, through which thejet gases flow in the direction of the arrow 39.

The members 43 are braced by aerofoil struts 49, which are made fast inthe adjacent exterior surfaces of the members 43.

The flow-dividing members 42, 43 are of a semielliptical shape which hasbeen found especially suitable for resisting the loading applied to thesaid members by the pressure of the hot gases. The semi-elliptical shapealso provides the exteriors of the members 42, 43, in longitudinalsection, with a good streamline form such as is adapted to the gas flowand therefore such as to keep the thrust loss low.

It will be noted from FIGURE 1 that the flow-dividing members 42, 43 areprovided with inner skins 42, 43' respectively which are shaped to suitthe flow of atmospheric air, the shape of the members 42, 43 being suchthat only relatively minor alteration of their interiors is required tomake them suitably shaped for atmospheric air flow therethrough. Theshaping of the members 42, 43, 42', 43 shown in FIGURE 1 is designed toresult in low external drag.

The jet nozzle 40 can be attached, as shown in FIG- URE 3, to the jetpipe 50 of a gas turbine engine 51.

In operation, gases flowing through the jet pipe 50 will pass out of thejet nozzle 40 through the channels 48 formed between adjacent members 42and 43, and also through the central space between the members 43.

Air will be entrained by the guide vanes 45 toenter the apertures 44 andflow through the interior of members 43. Similarly, air will beentrained through guide vanes 47 to enter apertures 46 and flow outthrough the open downstream ends of members 42. Atmospheric air will mixwith the jet gases at the boundaries formed by the downstream ends ofmembers 42 and 43.

We claim:

1. A jet noise suppressor nozzle comprising a tubular casing memberhaving a plurality of hollow, first flowdividing members on the interiorof said tubular member and arranged about the interior thereof, each ofsaid members having a closed upstream end merging with said tubularmember and the downstream end extending inwardly and being open, andhaving communication with an opening in said tubular member upstreamfrom said open end, and said tubular member having at least one secondflow-dividing member between adjacent first flow-dividing members, saidlast named dividing members being similar to but of smaller dimensionsthan said first flow-dividing members, and circumferentially spacedtherefrom for the flow of jet gases therebetween.

2. The jet noise suppressor nozzle as defined in claim 1 in which theratio, at the downstream end of the nozzle of the two cross-sectionalareas within the nozzle casing which are respectively disposedexternally and internally of the flow-dividing members being within therange of 121.75 to 1:20.

3. The jet noise suppressor nozzle as defined in claim 1 having means onsaid casing for entraining atmospheric air, flowing externally of thenozzle casing through said openings and into the interior of at leastsome of said flow-dividing members.

4. The jet noise suppressor nozzle as defined in claim 3 in which saidmeans comprise guide vanes carried by the casing and positioned acrossthe openings to direct said air into and through the flow-dividingmembers to mingle with the jet gases downstream of the nozzle.

5. The jet noise suppressor nozzle as defined in claim 1 in which saidflow-dividing members are uniformly circumferentially spaced about thenozzle casing, extend radially inwardly therefrom to increasing depthfrom upstream to downstream ends and increase similarly in width, thespaces between said flow-dividing members extending radially inwardly tomerge with an unobstructed central axial passage through said nozzle.

6. The jet noise suppressor nozzle as defined in claim 1 in which airfoil section struts interconnect adjacent flow-dividing members whichextend fartherest radially inwardly and pass over and clear of theintervening members of smaller dimensions.

References Cited in the file of this patent UNITED STATES PATENTS2,358,690 Decker Sept. 19, 1944 2,389,059 Kurth Nov. 13, 1945 2,504,422Johnson et al. Apr. 18, 1950 2,553,443 Davis May 15, 1951 2,944,624Morley July 12, 1960 2,982,092 Keen May 2, 1961 FOREIGN PATENTS 997,262France Sept. 12, 1951 768,553 Great Britain Feb. 20,

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